Servo-integrating stabilizer

ABSTRACT

In an optic stabilizer having case mounted optic elements and a complementary and movable optical element for stabilizing an image, an apparatus for imparting improved stabilizing motion to the moving optical element is disclosed. The movable optical element, typically a mirror, is mounted for two degrees of motion relative to a neutral position along the optic axis. A variable torque field, typically magnetic, is provided to pass through the optical element and to urge the optical element back to its neutral position. By the expedient of providing a sensor for detecting misaligned positions of the movable optical element and integrating on a time average basis the misaligned position of the movable element, the magnitude and polarity of the variable torque field can be controlled to provide improved stabilizing motion of the movable optical element.

FIPB

I United States Patent 1 1 .1111 3,756,686 Humphrey 1 Sept. 4, 1973 lSERVO-INTEGRATING STABILIZER Primary Examiner-David H. Rubin 75 l t.Wlll E." h ,Okl d, l 1 men or f my a an Attorney-Townsend & Townsend[73] Assignee: Optical Research and Development Corporation, Oakland,Calif. ABSTRACT 22 il Sept, 8, 1971 ln an optic stabilizer having casemounted optic elements and a complementary and movable optical ele- [211 Appl' ment for stabilizing an image, an apparatus for impartingimproved stabilizing motion to the moving optical 52 US. Cl. 350/16,250/201 element is disclosed- The movable optical element, y 51 1m. 01.G02b 23/00 isally a mirror, is mounted for two dssrees of motion 58Field of Search 350/16; 250/201, relative to a neutral Position alongthe Optic axis A 250/213 214; 355 141 143 149 243 250; variable torquefield, typically magnetic, is provided to 3 3 204 1 224 pass through theoptical element and to urge the optical element back to its neutralposition. By the expedient 5 R f n e Cig d of providing a sensor fordetecting misaligned positions UNITED STATES PATENTS of the movableoptical element and integrating on a 00 time average basis themisaligned position of the movgz 'ggg m g" able element, the magnitudeand polarity of the vari- 2/1970 5; "250/20! able torque field can becontrolled to provide improved 3:5l8:016 6/1970 Burma Lilli: I: 356/248Stabilizing mmable Pticall element- 2,479,309 8/1949 Cave-Browne-Cave250/201 3,532,409 10 1970 Humphrey 350/16 16 5 PATENTEO 4 m3 Z INVENTOR.

WILLIAM E. HUMPHREY Q j BY ATTORNEYS PAIEIIIEII H' 3.756.686

SPRING CONSTANT MIXED I OUTPUT AMPLIFIER E DIFFERENTIAL OUTPUT 92; lg s97 INTEGRATOR .L 92 OUTPUT CONTROL s 5 5 J I02 {Q T CONTROL INVENTOR.

WILLIAM E. HUMPHREY BY FIG 4 TWMTW ATTORNEYS SERVO-INTEGRATINGSTABILIZER This invention relates to optical stabilizers so that opticalinstruments of high power can be stabilized against image vibration whensubjected to instrument vibration from accidental angular motion alongangular coordinates orthogonal to the optic axis. More particularly,this invention relates to a method and apparatus for providing timeaveraged stabilizing motion to a movable optical element having twodegrees of free dom relative to an optic axis.

Hand held optical instruments of high power cannot be used whensubjected to accidental angular motion. Such instruments often receivesuch ambient accidental angular motion from the tremulation of the humanhand. This ambient accidental angular motion causes an image motioninterior of the instrument directly proportional to the increased poweror focal length of the instrument. Hence, the magnified image, becauseof its motion, cannot be observed or accurately recorded.

Optical stabilizers correct these problems. These optical stabilizershave typically included two sets of optics. First, case mounted opticalelements are mounted to the case and move with the case. Second, movableoptical elements are stabilized with reference to space either byremaining stationary with respect to a spatial reference or by movingproportionately with respect to a spatial reference. The combined effectof the movable optic elements and case fixed optic elements are chosento produce image motion equal and opposite to the image motion producedby the accidental angular motion. Image stabilization results.

The movable optical elements have heretofore been mounted in fluid bathsand typically coupled to the case by a small spring force--such as thatprovided by a magnet or elastic band. The spring and fluid bath combineto provide space referenced connection when the instrument is subjectedto the relatively high frequency vibrations of small accidental angularmotion and yet permit panning of the instrument when the instrument issubjected to low frequency angular movement.

The prior art method of controlling the movable optical elements topermit their stabilized motion has been limited. Typically, theselimitations have arisen from the necessity of keeping the springconstant of the spring force as small as possible, yet large enough tomask spurious torques introduced into the system. These spurious torqueshave heretofore been generated by variations of environmental conditionsof the instrument and the construction imbalances of the instrument.Such variations and imbalances produce misalignment of the movable opticelements both in stationary positions and when the movable elements arein motion.

These spurious torques can be easily understood. For example if a mirroris used as the movable optic element and supported with neutral bouyancyin a fluid,

a small offset of the center of floatation of the mirror and the centerof gravity of the mirror will result in a gravity reference pendulousmotion of the mirror which decenters the optical system and degrades theoptical performance. Moreover, if the optical instrument is used on acold day then the warmth of the human hand can generate in thesupporting fluid bath thermal flow of fluids, changes in viscosity, andchanges in fluid density. Mirror movement will vary. Additionally, ifthe spring force is applied by external magnet field of relatively lowstrength, ambient fields can upset the positioning of the mirror.

An object of this invention is to provide a restoring torque for amovable optic element which varies in proportion to the time averagedangular displacement of the movable optic element with respect to opticinstruments. Typically, sensors detect the misalignment of the opticelement. These sensors provide outputs to an integrator which throughamplification provides a time average restoring torque, typicallythrough magnetic fields, to the misaligned optical element.

An advantage of this invention is that a relatively high spring constantis no longer required to mask spurious torques due to pendulous mirrorimbalance, thermal fluid flow, change of fluid viscosity, change offluid density, or even the presence of external magnetic fields.

Another advantage of this invention is that it can be used to align amirror, a telescope, or other moving optical elements in a stabilizedoptical train.

A further advantage of this invention is that a correctional torque isapplied to the moving optical element at conditions of imbalance only.When the mirror is aligned, torque need not be applied.

Still another advantage of this invention is that the spring constantfor correcting the movable optic element to a neutral position can berelatively low. The movable optical element can be stabilized forinstruments of increasingly higher power. Improvement of stabilizedoptic element response to instrument motion over conventionalspring-fluid systems increases through reduction of the effectiverestoring force by a factor of as much as 60.

Yet another advantage of this system is that the optical element can bemounted in a transparent fluid bath. It can be provided with buoyantneutral support as well as a high shock resistant mounting.

Yet another object of this invention is to combine with the time averagecontrolled movement of the mirror, an analog of a spring constant forkeeping the mirror centered and a velocity factor to influence dampingof the mirror movement responsive to instrument panning.

An advantage of these analogs is that they can be adjusted for changedmechanical operating conditions interior of the instrument. For example,when the thermal environment of the instrument has changed the viscosityof the fluid in the bath, adjustment of the analog can compensate forsuch a changed condition.

Yet another object of controlling the movement of the movable opticelement is to provide a torque system which will not load the bearingsholding the movable optic element on the optic axis. Thus angularmovement of the movable optic element will not be accompanied byincreasing bearing load.

An advantage of this magnetic field is that the mechanical andelectrical components for holding the moving optical element on theoptic axis can be minimized.

Still another object of this invention is to provide a read-out of themisalignment of the movable optical element with reference to caseorientation at any given instant in time.

An advantage of this aspect of the invention is that if the case fixedoptical elements are bore sighted (as in a gun sight application), themoving optics can be referenced to the bore sight. An opticallystabilized gun sight mounted on an unstable platform (such as a tank) isfeasible.

An advantage of this invention is that virtually any detector, such a aninfra-red detector which comprises an optical element can be centeredwith respect to a bore sight.

Yet another object of this invention is to provide a loaded tankcircuit, metal detector to determine misalignment of the mirror.According to this aspect, the field displacement of a small disc ofmetal mounted to the back of a mirror is sensed by a metal detector.

Yet another object of this invention is to provide for a light sensitivearray to detect misalignment of the mirror. According to this aspect ofthe invention, a mirror is mounted on the back surface of the opticalelement. Light is impinged on the mirror and reflected to sensors. Thesesensors detect the misalignment of the mirror.

An advantage of this light sensitive displacement detector is that thelight detectors can be placed in a bridge circuit. Misalignment of themirror results in electrical currents of reversible polarity. Theseoutputs thus can by their polarity indicate the direction of movementand by their intensity the amount of movement.

Yet another object of this light sensitive displacement detector is thatit is insensitive to external magnetic or electrical fields. Thedetector is sensitive only to light which can be easily screened fromeffecting the device by the use of opaque materials. Additionally,optical filtering of the light array can be used to discriminate againstambient light present in the instrument.

Yet another object of this invention is to provide for an adjustedneutral position of an optical element without the consumption ofelectrical power.

An advantage of this neutral positioning is that long battery life canbe provided to aportable hand held instrument.

An additional object of this invention is to provide for mechanicaltorquing of the movable optic element.

An advantage of this mechanical torquing of the optic element is thatthe position of the mirror can be independent of magnetic and electricalfields.

Still another object of this invention is to set forth a group offactors for controlling the integration factor, spring constant, andvelocity factor in a fluid immersed instrument so that stable operationof the device will occur.

Other objects, features and advantages of this invention will becomemore apparent after referring to the following specification anddrawings, in which:

FIG. l-is a schematic isometric view illustrating a hand held telescopeof high power of magnification which can be used with this invention;the movable optical element here being shown as a mirror provided withneutral buoyant support interior of a transparent fluid bath;

FIG. 2 is an expanded view of the rear surface of the movable opticalelement (mirror) of FIG. 1 with detectors for sensing the misalignment,motor driven rheostats for supplying a power output proportional to theoff axis position of the mirror; and magnets for supplying to thepermanently magnetized optical element a variable torque to position theelement with reference to space;

FIG. 3 is a perspective similar to FIG. 2 showing an alternateelectrical control in which light is used to detect misalignment of theoptical element and an electrical analog circuit is used to provide alinear spring type output, a velocity factor output and a time averagedoutput for control of the mirror motion;

FIG. 4 is a perspective view similar to FIGS. 2 and 3 wherein thecontrol of the magnetic fields occurs by permanent magnets interruptingthe gap between a magnetic field conducting core to provide forpennanent torque on the mirror without the consumption of energy; and

FIG. 5 is a schematic perspective view showing in partial section anapparatus for applying mechanical torque to center a movable opticelement, here shown as a mirror.

With reference to FIG. 1, a typical optical stabilizer is illustrated.Briefly stated, the stabilizer is a 20 power optical train having anobjective lens A mounted to focus light onto a movable optic element,here shown as mirror B. Mirror B is balanced for buoyant neutral supportinterior of a fluid bath C and contained interior of a chamber D.Stabilized light from mirror B is directed onto inverting mirrors Ewhere the light is subsequently imaged at a plane F and viewed throughan eyepiece G. For convenience, a negative lens 14 is shown placed inthe optic path to extend the focal length of the optic path. The opticsof the stabilizer will not be fully set forth. These optics are fullydiscussed in my copending U.S. Pat. application Ser. No. 75,965, filedSept. 28, 1970, entitled SEMI-ACHROMATIC STA- BILIZER UNIT, Pat. No.U.S. Pat. 3,711,178, issued Jan. 16, 1973.

In operation, the image stabilizer will view a distant object 0, hereshown schematically as the figures of a tree and a man. When viewed bythe eye of an observer, an image I which is magnified by 20 power willbe observed. When the instrument is subjected to accidental angularmotion during such viewing, the stationary optical elements (A, E, 14and G) and the movable optical element, mirror B, will combine toproduce a stabilized image. It is the control of the movement of mirrorB which is the subject matter of this invention.

Referring to FIG. 2, a control for positioning mirror B is schematicallyillustrated. Typically, mirror B is balanced for neutral buoyant supportinterior of chamber D (shown in broken lines in FIG. 2) within fluidbath C (not shown for clarity of illustration in FIG. 2). Typically, themirror is suspended on a band 16 attached to a window 18 on the forwardend of chamber D and secured to the back circular wall 20 at the rearend of chamber D.

A permanent magnet J is attached to the rear surface of mirror B. MagnetJ produces a magnetic field along the axis of band 16 when mirror B isin the neutral position. As shown here the magnetic field of permanentmagnet J is polarized north (N) in the direction of window l8 and south(S) in the direction of the rear circular wall 20 of chamber D.

Torque is applied to mirror B through variable magnetic fields. As hereshown, a variable magnetic field emanating from a field conducting coreK in the vertical axis and a field conducting core L in the horizontalaxis torques mirror B by a couple to the permanent magnetic field ofmagnet J.

Before the control of the variable intensity magnetic field can bediscussed, the detection of the off-axis movement of mirror B relativeto chamber D must be illustrated. Typically the rear surface of mirror Bis provided with a small, fiat, metallic ring concentrically mountedabout the axis of band 16 as it is threaded through the mirror 8. Theposition of this metallic ring is detected by two loaded tank circuitmetal detectors 27 and 29 mounted with their detecting coils 31 and 33interior of chamber D and within the fluid bath C.

Loaded tank circuit metal detectors 27 and 29 are oscillators which varyin their oscillating output directly proportional to the proximity ofring 25 from their respective detector coils 31, 33. These detectors arepre-referenced to emanate a voltage of a first polarity when ring 25 isremote from their respective sensing elements 31, 33, to emanate avoltage of a second polarity when ring 25 is proximate their respectivecoil sensors 31, 33 and to emanate no voltage when ring 25 and itsattached mirror B is in a neutral position.

Loaded tank circuit metal detectors are known. Specifically, a tankcircuit metal detector which can easily be modified for use with thisinvention is described in publication entitled How to Build ProximityDetectors and Metal Locators" by John Potter Shields and published byHoward W. Sams &. Co., Inc., of Indianapolis, Indiana, at pages 96through 100.

As is apparent, loaded tank circuit metal detector 27 detects thedeflection of mirror B in the vertical axis. Its operation to vary themagnitude and polarity of the magnetic field emanating from fieldconducting core K can now be set forth.

Typically, the output of detector 27 will be channeled to a directcurrent motor 35. Obviously when current of a first polarity is receivedat motor 35, rotation of motor 35 in a first direction will occur.Conversely when an electrical signal of a reversed polarity is receivedat motor 35, rotation of the motor in a second direction will occur.

Motor 35 is coupled through concentrically mounted reduction gearing 37and shaft 39 to control the position of a potentiometer 40.Potentiometer 40 has an applied electrical bias. This bias emanates froma ground connection 41, a power source 42 for applying positive voltageto one end of the winding of potentiometer 40, a power source 44 forapplying negative voltage to the other end 46 of the winding ofpotentiometer 40.

Shaft 39 will position the contact 48 of potentiometer 40. Typically,when contact 48 is positioned intermediate ends 45, 46 of the winding ofpotentiometer 40, zero voltage will be tapped from the coil. As contact48 moves towards end 45 of the winding of potentiometer 40, anincreasingly positive voltage will be tapped from the coil. This is theposition of the contact shown in FIG. 2. Conversely, when contact 48moves towards end 46 of the winding of potentiometer 40, an increasinglynegative voltage will be tapped from the coil.

The output of contact 48 is connected in series to a a coil 50 woundabout magnetic field conducting core K.

The magnitude and direction of the current received at coil 50 willdetermine the magnitude and polarity of the magnetic field imparted bythe core K. Core K will thus torque mirror B. This torquing will occurthrough the couple on the permanent magnetic field emanating from thepermanent magnet J attached to the back end of the mirror.

For example, when contact 48 is in a position to tap the winding ofpotentiometer 40 at a position where the winding has a positivepotential, core K will be polarized so that its lower arm 55 will be anorth magnetic pole while its upper arm will be a south magnetic pole.Conversely, when contact 48 taps the winding of potentiometer 40adjacent the end 46 of the coil for a negative potential, lower arm 55of core K will be a south magnetic pole while upper arm 57 will beprovided a north magnetic pole.

Dependent upon the magnitude and polarity of the magnetic fieldemanating from core K mirror B will have a torque applied to it. In thecase where contact 48 taps the positive section of the winding ofpotentiometer 40, the mirror will be biased to rotate clockwise. This isto say, when viewed from the side of the instrument, the top edge ofmirror B rotates toward the upper arm 57 and lower edge of mirror Brotates away from the lower arm 55. Conversely, where contact 48 taps anegative portion of the winding 45 of potentiometer 40, the mirror willbe biased to rotate counterclockwise.

Just as detector 27 through motor driven potentiometer 40 and controlcoil 50 controls the polarity of the field emanating from core Kdetector 29, potentiometer 60, and coil can be made to control themagnitude and polarity of a magnetic field emanating from fieldconducting core L. Field conducting core L will torque mirror B about avertical axis normal to the axis of band 16 as it is threaded throughmirror B.

Several observations can be made about the embodiment of the inventionas it is illustrated in FIG. 2. First, it will be understood that themotor driven potentiometers 40, 60 serve only to apply an integratedtorque to restore mirror B to a neutral position. This torque isgenerated from a time averaged position of mirror B off a neutralposition. So long as mirror D has a position away from the neutralposition, motor 35 and its control rheostat 40 will generate anincreasing torque by field conducting core K. This torque will increasewith increasing time. When the mirror returns to the neutral position,the torque will no longer increase. Its intensity will be maintainedconstant as of the time it returns to a neutral position, Thus, theapplied torque can be said to be time averaged, the time averaging beingthe sum of the movement of the mirror from its neutral position timesthe time increment that it is away from its neutral position.

Control of the magnitude of the time integrated torque applied to mirrorB can be through several expedients. For example, the output signal ofthe tank circuit detectors 27, 29 can be raised or lowered to controlmirror torque. Additionally, the voltage applied to the windings of thepotentiometers 40 or 60 can be controlled.

The reduction gearing used in driving the motor driven potentiometers40, 60 has an advantage not immediately apparent. Typically, suchgearing includes a stiction factor; a predetermined torque must beapplied through the motor before any movement of the controlled contactof the motor driven potentiometer 40 or 60 occurs and the stiction ofthe gears is overcome. Thus, the tendency of the control mechanism ofthis invention to hunt on either side of the neutral position of mirrorB will be damped by the stiction factor of the bearing.

The positioning of the mirror 8 and its attached permanent magnet Jrelative to the magnetic field conducting cores K and L is alsoimportant. Typically, these cores conduct the magnetic field in an arebetween their respective ends. For example, if the upper arm 57 of coreK is polarized north, and the lower end 55 of core K is polarized south,the north-south magnetic field will follow an arcuate path between therespective ends of the core. By positioning mirror B towards and awayfrom the ends 55, 57 of field conducting core K, a position of mirror Bwill be reached where mirror B is neither urged towards or away fromcore K. Thus, it will be seen that although the variable mag neticfields emanating from core K can torque mirror B, it will not serve tourge mirror B along the optic axis along band 16.

It will additionally be realized that detectors 27, 29 will provide atall times a read-out of the off-axis position of mirror B relative tothe fixed elements of the optical train (shown as objective lens A,inverting mirrors E, negative lens 14 and eyepiece G in FIG. 1). Thissignal read-out of the angular difierence between a line of sight takenthrough the stationary optics and the mirror position can be convertedto an error signal. This error signal is directly proportional to theoffset of the line of sight through the optics of FIG. 1 relative to theneutral axis 75 of the optics of FIG. 1. With such an error signal thedevice according to this invention can be applied to gun sight and firecontrol applications.

With reference to FIG. 3 two alternate embodiments of this invention areshown. An optical sensor M is shown for sensing the off-axis position ofmirror B. Additionally, analog circuitry N is shown for introducing morerefined motion to mirror B through the magnetic field conducting cores Kand L.

The optic sensor M will first be set forth. Mirror B is mounted in amanner precisely analogous to that shown in FIG. 2. Permanent magnet Jhas affixed to the obverse side of the reflecting surface of mirror B asmaller mirror P. Mirror P is typically aligned parallel to therefleeting surface of mirror B (hidden from the view in the perspectiveview shown in FIG. 3).

,Typically, a solid state light source Q is used. Light source Q. isplaced and aligned in a horizontal plane intersecting the axis of theband 16 passing through mirror B. Typically, solid state light source Qis aimed to impinge its beam at an angle of approximately 45 in thecenter of the mirror P when the mirror assembly B is in the neutralposition. It will thus be understood that the light path from the lightsource passes along a path in an imaginery horizontal plane passingthrough the axis of the band 16 to the mirror P.

At mirror P, the light from light source Q will be reflected at an angleof reflection which is equal and opposite to the angle of incidence ofthe light upon the mirror P. Typically, movement of the mirror Prelative to the imaginery horizontal plane defined by the axis of band16 in the path of light between light source Q and mirror P will produceresultant movement of the reflected ray. As will hereinafter be seen,detection of the resultant movement of the reflected ray will result ina signal proportional to the movement of mirror B angularly about theimaginery horizontal plane.

Detection of the reflected rays occurs at two photosensitive detectors80 and 81. Detectors 80 and 81 are oriented a preselected distance apartand pointed towards the neutral position of mirror P. Typically, theyare disposed within the imaginery horizontal plane including the lightpath between light source Q and mirror P and including the axis of band16 as it passes through mirror assembly B. Photodetector 80 is shown tothe left of the neutral and reflected light path 83 from mirror P.Photoedetector 81 is shown to th right of the neutral and reflectedlight path 83 from mirror P. Both detectors are converged towards mirrorP at the incident location of the light path 82 from light source Q.

Detectors 80 and 81 can be of the photovoltaic or photoconductivevariety. As here shown they are of the photoconductive variety.

It is most conveient if detectors 80 and 81 are placed in a bridge-typecircuit. Such a circuit is illustrated and includes a power source 85, aresistor 86 connected in parallel across the power source with agrounded and adjustable center tap 87. Detector 80 is typicallyconnected in series with the positive output of power source 85.Likewise, detector 81 is connected in series with the negative output ofpower source 85. Detectors 80 and 81 are directly connected to an output88.

When mirror assembly B is in the neutral position, and detectors and 81have been positioned equidistantly on opposite sides of the reflectedlight path 83 from mirror P, the center tap 87 on resistor 86 isadjusted so that there is a neutral voltage potential on output 88. Oncethis adjustment is made, rotation of the mirror about an axisperpendicular to a plane through incident light path 82 and reflectedlight path 83 can be easily detected.

Assuming that mirror B rotates a small amount clockwise about axis 90,it will be seen that the reflected ray 83 is deflected away fromphotodeteetor 81 and towards photodeteetor 80. Typically, the bridgecircuit will become unbalanced. As photodeteetor 80 is of thephotoconductive variety, it becomes less of a resistance when light isincident upon it. Typically, the voltage output 88 will be morepositive.

Similarly, when mirror assembly B rotates counterclockwise about an axis90, movement of the reflected light ray 83 away from the detector 80 andtowards detector 81 will occur. The photoconductive path throughdetector 81 will become of low resistance and output voltage 88 will beless positive (for example a negative voltage may be emitted).

it will thus be seen that for clockwise positioning of mirror B about anaxis 90 away from a neutral position will result in a more positivevoltage being imparted to output 88. Conversely, a counterclockwisemovement of mirror B from its neutral position will result in a lesspositive voltage being imparted to output 88. As will hereinafter beseen, the polarity, rate of change, and time average of this voltagewill control the movement of mirror B through the analog circuitry N.

Analog circuity N can be reasily described. Output 88 is typicallyconnected in parallel to an integrator output, a differential (orvelocity) output, and a spring constant output. These are denominated assuch of the schematic drawing of FIG. 3. To control the input to each ofthe analog circuits there is connected in each of the analog circuits acenter tap resistance 92. Each of these center tap resistances 92 isconnected at one end to output 88, at the opposite end to a groundconnection and at the center tap to the analog circuitry. By adjustmentof each center tap, the input to each analog circuit can be controlled.This individual control allows adjustement for variations in mirrorbuoyancy, ambient magnetic fields and the like.

The integrator analog circuitry can be easily understood. Typically, acapacitor 94 is series connected between a ground connection on one handand the output from the center tap of the center tapped resistor 92.Voltage change of output 88 at the integrator output will be the same asthat voltage received at output 88 with only the resistance of thecenter tapped resistor, the resistance of the charging resistor 93 andthe integrating capacitor 94 effecting a change on the intensity andrate of change of the signal at the integrator output.

The differential (or velocity) analog circuitry of mirror B relative tothe stationary optics can also easily be understood. Typically, thecenter tap of the resistor 92 is connected in series across a capacitor96. The output of capacitor 96 is bled off to ground through a resistor97. When a high rate of change of mirror B relative to the stationaryoptics occurs, a voltage will be induced by capacitor 96 across resistor97. This differential or velocity output will be a function of the rateof change, of the size of capacitor 96, and the bleed off providedthrough ground connected resistor 97.

The analog spring constant is also easily understood. Assuming that aband 16 has an extremely weak spring factor, it should be noted that itis possible to generate on an analog basis a spring factor. Typically,the center tap of resistor 92 is connected to ground through aresistance 98. The value of resistance 98 as well as the adjustement ofthe center tap on center tap resistance 92 will provide the desiredspring factor. It will be seen that this output will be directlyproportional to the offset of mirror B relative to its neutral positionof rotation about axis 90.

Typically, the spring constant output, the differential or velocityoutput, and the integrator output are all mixed and thereafteramplified. As mixers and amplifiers capable of accepting a voltagesignal and generating a direct current signal of the desired polarityand intensity are well known in the art, they will not be furtherdiscussed here.

Typically, the mixer and amplifier illustrated in block form in FIG. 3will have an output to coil 70. As heretofore explained with referenceto FIG. 2 coil 70 will generate in core L a magnetic field of desiredpolarity and intensity. This magnetic field will apply a torque tomirror B serving to restore mirror B to a neutral position.

It will e understood that the rotation of mirror B here has beendescribed about a vertical axis 90 through the neutral position of band16 centering the mirror assembly B. Rotation of the mirror about ahorizontal axis orthogonal to an axis through the neutral position ofband 16 and axis 90 will be precisely analogous with the output of themixer and amplifier being directed to field conducting core K. Forclarity of illustration the additional detectors M required in verticalalignment orthogonal about detectors 80, 8] and appropriate analogcircuitry N for these detectors have been omitted.

It should be emphasized that the integrator output,

' differential output and spring constant output do not necessarilycombine at all instants in time to oppose mirror motion. As will beapparent to those skilled in phsycis,, they may combine to urge mirrormotion in the direction of mirror motion at a given instant of time. Inthis way circuits can be said to complement mirror motion. physics,

Moreover, due to changing instrument ambients, such as increasing ordecreasing temperature, adjustment of the control circuitry responsiveto the temperature change may result in velocity dependent torques notfound in nature. These torques can include torques acting in thedirection of the angular velocity of the movable element as well astorques moving against the angular velocity of the movable element. Inthis way the combined electrical and mechanical characteristics can bemixed to provide constant and predictable operating characteristics overwide variations of operating instrument ambients.

It will be reaslized that virtually all of the mirror positioning heredescribed requires a constant output of electrical current. Withreference to FIG. 4 an appara tus is schematically illustrated in whicha continuous output of current is not required for mirror positioning.

Referring to FIG. 4, a loaded tank circuit metal detector 27 is shownwhich is precisely analogous to that illustrated in FIG. 2. Metaldetector 27 detects the proximity of a metallic ring 25 on the backsideor nonreflective surface of mirror B. Assuming a deflection of mirror Boccurs, the intensity and polarity of the output of detector 27 willcause rotation of a motor 35 in a direction and rate proportional to thepolarity and intensity of the output signal. As previously illustrated,motor 35 through reduction gearing 37 is connected to a shaft 39 whichrotates at a reduced speed.

Shaft 39 typically has connected to it a permanent north-south magnet102. This magnet is placed within a gap defined within magnetic fieldconducting core K.

The north-south axis of permanent magnet 102 is shown transverse of thefield conducting axis of core K and this is in a neutral position asviewed in FIG. 4. Assuming that signals received from metal detector 27indicate a need for an angular deflection of mirror assembly B clockwiseabout an axis 107, permanent magnet 102 will be rotatedcounter-clockwise. The north pole of the magnet will be disposeddownwardly and towards the end 55 of the field conducting core K.Similarly the south pole of the magnet will be deflected upwardly andtowards the upper end 57 of the field conducting core K. A clockwisetorque will be exerted on mirror assembly B.

It should be understood that once a neutral position of mirror B hasbeen reached, motor 35 and shaft 39 will no longer rotate. Permanentmagnet 102 will remain at rest imparting to field conducting core K itspermanent magnetic field. This magnetic field will be sifficient to holdmirror B in its neutral position. No electrical energy output will berequired to maintain the mirror in its neutral position.

The torquing of mirror B by field conducting core L is preciselyanalogous. For purposes of brevity it will not herein be discussed.

Thus far, the torquing of the mirror assembly B has been illustratedwith a magnetic couple between a variable magnetic field external of themoving optic element and a permanent magnetic field attached to theoptic element. It should be apparent to the reader that the relativepositions of these magnetic fields can be reversed. Moreover, themovement of the optic element can be urged by virtually any other knownfield or force. For example, in FIG. 5 a mechanical means of orienting amirror assembly B in chamber D is dis closed.

With reference to FIG. 5, chamber D is shown in section filled withfluid C. A mirror centering band 16 centers mirror assembly D to apreselected position interior of the chamber. Mirror B is threaded toand affixed to a band 16 passing concentrically through the axis of thecylindrical chamber. At the forward end of the chamber band 16 ismounted to a post 111 affixed to the fluid exposed surface of window 18.At its opposite end, band 16 is fastened to a second and moving post114.

Post 114 is mounted for movement. Typically, post 114 is captured by thecenter of a concentric diaphram 110. Diaphram 110 is in turn mounted toa concentric aperture 112 in rear wall 20 of chamber D.

Diaphram 110 is affixed in fluid-tight relation across the aperture 112in chamber D, and prevents fluid flow from the interior of the chamberto the exterior of the chamber while permitting flexible movement of rod114. Deflection of the end 120 of rod 114 remote from the interior ofchamber D occurs by orthogonal rack and pinion drives 121 and 122. Forpurposes of brevity the vertical rack and pinion drive 121 will be theonly drive discussed.

Outward end of rod 120 is typically captured interior of an elongatering 125 having a horizontally extending aperture 126 through which end120 of rod 114 is placed. Ring 125 is in turn rigidly mounted to rod 128held for vertical sliding movement by guides 130 at upper end of rod 128and at the lower end of rod 128. As is apparent limited vertical up anddown movement of the rod 128 can occur and will produce a correspondingup and down movement of elongate ring 125. The elongate ring through theaperture 126 will impart a corresponding up and down movement to the end120 of rod 114.

Naturally, it will be desired to produce a corresponding horizontalmovement from horizontal rack and pinion drive 122. As can be seen slot126 in elongate ring 125 will permit such horizontal movement whileimparting to the end 120 of rod 114 the desired vertical movement.

Assuming that rod 114 at its end 120 has been deflected upwardly, thisrod will tend to pivot about its concentirc attachment through theinterior of diaphram 110. A corresponding downward deflection of theopposite end of the rod 135 interior of the fluid bath C will occur.When end 135 of rod 114 rotates downwardly, it will cause a clockwisetorque to be imparted to mirror assembly B.

It can be immediately seen that with the detector 27 motor 35 andreduction gearing 37 previously described, the mechanical movement ofmirror B can be easily urged. Moreover, the introduction ofanalogcircuitry similar to that shown in FIG. 3 can easily be made.

The examples of inertial motion of the mirror B and of the torquing ofthat mirror can obviously be modified in many ways. For example, mirrorB could be coupled to a gyroscope and inertial motion of the mirrorurged through and by the gyroscope. In turn the motion of the gyroscopecould be altered by the circuitry disclosed herein to provide theimproved long term alignment properties herein described. It will beobvious to those skilled in physics that the input torques to thegyroscope will have to be orthogonally realigned to compensate for theprecession characteristics of the gyrsocope used.

The dynamic performance of a stabilizer system incorporating the ServoIntegrating Stabilizer concept bears some examination. In particular,theoretical examination of the amount of integrating that can beincorporated in the torquing system reveals that beyond a certain levelof integrating contribution, the stabilizer enters into a realm ofuncontrolled oscillation. This theoretical prediction has been born outin experiments with models having a variable integrating contribution tothe total torque on the stabilized component. The region of acceptableoperation can be predicted on the basis of a mathematical modelcorresponding in a reasonable degree with the performance of the actualembodiment of a servo integrating stabilizer although no manageablemodel is a perfect analog ot the real mechanical embodiment. Forexample, bearings may have small upredictable stiction,38 electronicsmay saturate at certain signal levels, or fluid flow may be complicatedby small local vortices. Nevertheless, these practical perturbationsnotwithstanding, useful limitations on the practical embodiments can beestablished for the gross performance of a servo integrating stabilizer.

The basic equation to consider is shown below:

This is a third order differential equation relating acceleration (Jr')of a body whose position (x), is subject to acting forces proportionalto velocity (i), position (x) and position integrated over time I 1 dt).In the case of a floated mirror, x would represent angular orientationof the mirror and A, B and C could be represented more specifically asfollows:

A k,/l

B k,/I

where l efi'ective moment of inertia of mirror-fluid system.

k torque per velocity (viscous type drag torque from fluid, proportionalto viscosity and float-tocase geometrical coupling, as well aselectrically generated torques proportional to velocity). k, spring likerestoring torque per angular position. k, 32 torque per time integratedangular position. f time varying torque inducing motion of float andincluding coupling of case vibrations to the mirror through the fluidand restoring forces as well as long term effects such as torquesgenerated with change in temperature, etc. For the purpose of thepresent discussion, the exact nature off(t) is not important. Thesolution of such a differential equation involves a particular solutiondescribing the response to the perturbing function f (r) as well as amore general homogeneous solution for the equation. This homogeneoussolution is of prime importance in regard to stability of the stabilizeras it is composed essentially of exponential terms of the form:

, where a represents roots of the equation:

These roots may be complex numbers; however, the real part of a is ofcritical importance because of positive real part indicates anexponential increase with time in the motion of the stabilizing element.Therefore, all combinations of A, B and C which result in a positivereal part of a must be excluded. Fortunately, this limitation can beexpressed in the relatively simple form:

I. AB must be greater than C. in addition ll. The coefficients, A, B andC are restricted to positive values. These conditions define a region ofuseful stabilizer constructions.

It should be understood that numerous modifications can be made withoutdeparting from the spirit of this invention. For example, the magneticfield conducting cores could be mounted interior of chamber D as well asexterior of chamber D. Moreover, virtually any mechanical, electrical ormagnetic arrangement for intro-- ducing torques to the mirror B could beused. Examples of this would include using electrostatic fields toprovide the centering force to the movable optic element. The fluid inwhich the mirror B is mounted could be changed or omitted in theentirety. Moreover, the mirror assembly could be gimbled and the fieldsproduced relied upon to give the entire movement to the mirror assembly.Further, the movable optic element could be of the variety that issubjected to displacement on and off the optic axis as well as angularmotion relative to the optic axis. Likewise, other modifications to thisinvention may be apparent to those having skill in the art.

What is claimed is:

1. In an optical stabilizer for observing an object along a light pathincluding: a case about an optic axis; stationary optic elements mountedto said case along said optic axis; a movable optic element mounted tosaid case in said optic axis, said movable optic element movableresponsive to inertial force to move said movable element towards andaway from a neutral position with respect to said optic axis responsiveto accidental angular motion of said case; said movable optic elementupon being moved by said inertial force having an optic effect toproduce image motion equal and opposite to image motion caused byaccidental angular motion of said optic axis through said case; andmeans for applying a moving force to said movable optic element relativeto said case for causing said movable optic element to return to saidneutral position when said case receives ambient accidental angularmotion, said means for applying a moving force attached to said case andcoupled to said optic element; the improvement in said means forapplying a moving force comprising: a sensor for detecting movement ofsaid movable optic element from said neutral position and emitting asignal indicating said movement; means for changing said applied movingforce to said movable optic element to complement movement of saidmovable optic element from said neutral position, said moving meansincluding at least a first control input for increasing and decreasingsaid moving force applied to said movable optic element; and, controlmeans communicated to said sensor to receive said emitted signal andhaving an output to the control input of said means for changing atleast a portion of said moving force to said movable optic elementresponsive to said emitted signal.

2. The invention of claim 1 and wherein said control means changes saidmoving force during the period of time that said emitted signalindicating movement from said neutral position is received from saidsensor.

3. The invention of claim 1 and wherein said control means has an outputto said control input for changing at least a portion of said movingforce proportional to said emitted signal indicating movement from saidneutral position.

4. The invention of claim 1 and wherein said control means iscommunicated to said sensor and has an output to said control input forchanging at least a portion of said moving force proportionally to thevelocity of said movable optic element with respect to said case.

5. An optical stabilizer for observing an object along a light pathcomprising: a case about an optic axis; stationary optic elementsmounted to said case along said optic axis; a movable optic elementmounted to said case in said optic axis, said movable optic element mov'able with respect to said optic axis responsive to inertial forces tomove said movable element away from a neutral position responsive toaccidental angular motion of said case, said movable optic element uponbeing moved by said inertial forces having an optic effect to produceapparent image motion equal and opposite to image motion caused byambient accidental vibrations being received at said case and angularlymoving said fixed optic elements with respect to said optic axis; andmeans for providing a force coupling between said case and said movableoptic element for urging movement of said movable optic element, saidmeans for providing said coupling including means for adjustably varyingat least a portion of the force of said coupling responsive to movementof said movable optic element from said neutral position.

6. The invention of claim 5 and wherein said coupling means includes amagnetic couple including a first permanent magnet and a second variablemagnet with one of said magnets being attached to said movable opticelement and other of said magnets being attached to said case.

7. The invention of claim 5 and wherein said means for varying the forceof said coupling on said movable optic element includes a member forapplying a mechanical torque to said movable optic element for urgingsaid movable optic element to said neutral position; and means forangularly realigning said member with respect to said optic axis tochange the torque on said member in a predetermined direction.

8. The invention of claim 5 and wherein said movable optic element ismounted for angular movement with respect to a point on said optic axisin two degrees of motion.

9. An optical stabilizer comprising: a case about an optical axis; atleast one stationary optical element mounted to said case along saidoptical axis; movable optic element mounted to said case on said opticaxis and movable responsive to inertial force to move said optic elementtowards and away from a neutral position on said optic axis, saidmovable optic element upon being moved by said inertial force having anoptic effect to produce image motion equal and opposite to image motioncaused by accidental angular motion of said optic axis through saidcase; and means for returning said movable optic element to said neutralposition on said optic axis; said moving means including a couple tosaid movable optic element between first and second points on eitherside of said movable optic element, said couple having an input changingthe force through said couple; and control means responsive to movementof said movable optic element towards and away from said neutralposition communicated to said input for varying the force of said coupleresponsive to movement of said movable optic element off said neutralpositionv 10. The invention of claim 9 and wherein said couple ismagnetic and includes a U-shaped magnetic field conducting core with oneend of said U terminating at said first point and the other end of saidU terminating at said second point, means for imparting a variablemagnetic field to said U shaped magnetic field conducting core; and apermanent magnet attached to said movable optic element.

11. The invention of claim 9 and wherein said means for imparting avariable magnetic field conducting core includes a gap in said U-shapedmagnetic field conducting core; a permanent magnet mounted within saidgap of said U-shaped magnetic field conducting core; means forpositioning said magnet to preselected orientations within said gap toimpart to said magnetic field conducting core a field of varyingpolarity and intensity.

12. The invention of claim 9 and wherein said couple includes aneleastic member passing between said first and second points and saidcontrol means includes apparatus for changing the position of at leastone of said points.

13. In an optical stabilizer for observing an object along a light pathincluding: a case about an optic axis; stationary optic elements mountedto said case along said optic axis, a movable optic element mounted tosaid case along said optic axis; said movable optic element movableresponsive to inertial force to move said movable element towards andaway from a neutral position with respect to said optic axis responsiveto accidental angular motion of said case; said movable optic elementupon being moved by said inertial force having optic effect to produceapparent image motion equal and opposite to image motion caused byaccidental angular motion of said optic axis through said case; andmeans for moving said movable optic element relative to said case forcausing said movable optic element to return to said neutral positionwhen said case receives ambient accidental angular motion, said meansfor moving including a detector having an input from said movable opticelement; the improvement in said de tecting means comprising: a surfaceon and mounted to said movable optic element; a transducer mountedadjacent said movable optic element for emitting a signal responsive tothe relative movement between said sensor and said surface on saidmovable optic element.

14. The invention of claim 13 and wherein said sensor includes a loadedtank circuit metal detector and said surface includes a metallicsurface.

15. The invention of claim 13 and wherein said sensor includes a lightsource, a photodetector and a light path therebetween; and wherein saidsurface includes a reflective surface disposed in said light pathbetween said light source in said photodetector.

16. The invention of claim 15 and wherein said sensor includes at leastfirst and second photodetectors; said first and second photodetectorspositioned with respect to said light source and said light paths to aposition intermediate said light path when said movable optic element isin the neutral position; bridge circuit means connected to saidphotodetectors for emitting first signal when said light path isintermediate said phtodetectors, emitting a second signal when saidlight path is more adjacent one photodetector than the other detectorand emitting a third signal when said light path is more adjacent theother of said photodetectors than said one photodetector.

i t i

1. In an optical stabilizer for observing an object along a light pathincluding: a case about an optic axis; stationary optic elements mountedto said case along said optic axis; a movable optic element mounted tosaid case in said optic axis, said movable optic element movableresponsive to inertial force to move said movable element towards andaway from a neutral position with respect to said optic axis responsiveto accidental angular motion of said case; said movable optic elementupon being moved by said inertial force having an optic effect toproduce image motion equal and opposite to image motion caused byaccidental angular motion of said optic axis through said case; andmeans for applying a moving force to said movable optic element relativeto said case for causing said movable optic element to return to saidneutral position when said case receives ambient accidental angularmotion, said means for applying a moving force attached to said case andcoupled to said optic element; the improvement in said means forapplying a moving force comprising: a sensor for detecting movement ofsaid movable optic element from said neutral position and emitting asignal indicating said movement; means for changing said applied movingforce to said movable optic element to complement movement of saidmovable optic element from said neutral position, said moving meansincluding at least a first control input for increasing and decreasingsaid moving force applied to said movable optic element; and, controlmeans communicated to said sensor to receive said emitted signal andhaving an output to the control input of said means for changing atleast a portion of said moving force to said movable optic elementresponsive to said emitted signal.
 2. The invention of claim 1 andwherein said control means changes said moving force during the periodof time that said emitted signal indicating movement from said neutralposition is received from said sensor.
 3. The invention of claim 1 andwherein said control means has an output to said control input forchanging at least a portion of said moving force proportional to saidemitted signal indicating movement from said neutral position.
 4. Theinvention of claim 1 and wherein said control means is communicated tosaid sensor and has an output to said control input for changing atleast a portion of said moving force proportionally to the velocity ofsaid movable optic element with respect to said case.
 5. An opticalstabilizer for observing an object along a light path comprising: a caseabout an optic axis; stationary optic elements mounted to said casealong said optic axis; a movable optic element mounted to said case insaid optic axis, said movable optic element movable with respect to saidoptic axis responsive to inertial forces to move said movable elementaway from a neutral position responsive to accidental angular motion ofsaid case, said movable optic element upon being moved by said inertialforces having an optic effect to produce apparent image motion equal andopposite to image motion caused by ambient accidental vibrations beingreceived at said case and angularly moving said fixed optic elementswith respect to said optic axis; and means for providing a forcecoupling between said case and said movable optic element for urgingmovement of said movable optic element, said means for providing saidcoupling including means for adjustably varying at least a portion ofthe force of said coupling responsive to movement of said movable opticelement from said neutral position.
 6. The invention of claim 5 andwherein said coupling means includes a magnetic couple including a firstpermanent magnet and a second variable magnet with one of said magnetsbeing attached to said movable optic element and other of said magnetsbeing attached tO said case.
 7. The invention of claim 5 and whereinsaid means for varying the force of said coupling on said movable opticelement includes a member for applying a mechanical torque to saidmovable optic element for urging said movable optic element to saidneutral position; and means for angularly realigning said member withrespect to said optic axis to change the torque on said member in apredetermined direction.
 8. The invention of claim 5 and wherein saidmovable optic element is mounted for angular movement with respect to apoint on said optic axis in two degrees of motion.
 9. An opticalstabilizer comprising: a case about an optical axis; at least onestationary optical element mounted to said case along said optical axis;movable optic element mounted to said case on said optic axis andmovable responsive to inertial force to move said optic element towardsand away from a neutral position on said optic axis, said movable opticelement upon being moved by said inertial force having an optic effectto produce image motion equal and opposite to image motion caused byaccidental angular motion of said optic axis through said case; andmeans for returning said movable optic element to said neutral positionon said optic axis; said moving means including a couple to said movableoptic element between first and second points on either side of saidmovable optic element, said couple having an input changing the forcethrough said couple; and control means responsive to movement of saidmovable optic element towards and away from said neutral positioncommunicated to said input for varying the force of said coupleresponsive to movement of said movable optic element off said neutralposition.
 10. The invention of claim 9 and wherein said couple ismagnetic and includes a U-shaped magnetic field conducting core with oneend of said U terminating at said first point and the other end of saidU terminating at said second point, means for imparting a variablemagnetic field to said U shaped magnetic field conducting core; and apermanent magnet attached to said movable optic element.
 11. Theinvention of claim 9 and wherein said means for imparting a variablemagnetic field conducting core includes a gap in said U-shaped magneticfield conducting core; a permanent magnet mounted within said gap ofsaid U-shaped magnetic field conducting core; means for positioning saidmagnet to preselected orientations within said gap to impart to saidmagnetic field conducting core a field of varying polarity andintensity.
 12. The invention of claim 9 and wherein said couple includesan eleastic member passing between said first and second points and saidcontrol means includes apparatus for changing the position of at leastone of said points.
 13. In an optical stabilizer for observing an objectalong a light path including: a case about an optic axis; stationaryoptic elements mounted to said case along said optic axis, a movableoptic element mounted to said case along said optic axis; said movableoptic element movable responsive to inertial force to move said movableelement towards and away from a neutral position with respect to saidoptic axis responsive to accidental angular motion of said case; saidmovable optic element upon being moved by said inertial force havingoptic effect to produce apparent image motion equal and opposite toimage motion caused by accidental angular motion of said optic axisthrough said case; and means for moving said movable optic elementrelative to said case for causing said movable optic element to returnto said neutral position when said case receives ambient accidentalangular motion, said means for moving including a detector having aninput from said movable optic element; the improvement in said detectingmeans comprising: a surface on and mounted to said movable opticelement; a transducer mounted adjacent said movable optic element foremitting a signal responsive to the relative movement between saidsensor and said surface on said movable optic element.
 14. The inventionof claim 13 and wherein said sensor includes a loaded tank circuit metaldetector and said surface includes a metallic surface.
 15. The inventionof claim 13 and wherein said sensor includes a light source, aphotodetector and a light path therebetween; and wherein said surfaceincludes a reflective surface disposed in said light path between saidlight source in said photodetector.
 16. The invention of claim 15 andwherein said sensor includes at least first and second photodetectors;said first and second photodetectors positioned with respect to saidlight source and said light paths to a position intermediate said lightpath when said movable optic element is in the neutral position; bridgecircuit means connected to said photodetectors for emitting first signalwhen said light path is intermediate said phtodetectors, emitting asecond signal when said light path is more adjacent one photodetectorthan the other detector and emitting a third signal when said light pathis more adjacent the other of said photodetectors than said onephotodetector.